A common misconception is that the irradiation of solids with energetic electrons and ions has exclusively detrimental effects on the properties of target materials. In addition to the well-known cases of doping of bulk semiconductors and ion beam nitriding of steels, recent experiments show that irradiation can also have beneficial effects on nanostructured systems. Electron or ion beams may serve as tools to synthesize nanoclusters and nanowires, change their morphology in a controllable manner, and tailor their mechanical, electronic, and even magnetic properties. Harnessing irradiation as a tool for modifying material properties at the nanoscale requires having the full microscopic picture of defect production and annealing in nanotargets. In this article, we review recent progress in the understanding of effects of irradiation on various zero-dimensional and one-dimensional nanoscale systems, such as semiconductor and metal nanoclusters and nanowires, nanotubes, and fullerenes. We also consider the t...

Ion and electron irradiation-induced effects in nanostructured materials

A model is presented for the development of breakdown in liquids subjected to uniform high amplitude electric field stresses with duration of microseconds or less. In this model, breakdown proceeds in four stages: (i) formation of a low density site (nucleation) in the liquid near an electrode, (ii) growth and expansion of this site until the local density is reduced below a critical density for electron impact ionization to take place, (iii) growth of an electron avalanche and its transformation into an ionizing front, and (iv) propagation of the ionization front via a sequence of processes occurring in the region ahead of the front; namely, heating by electron injection, lowering of the liquid density and avalanche growth and retardation. Expressions for the duration of each of these stages are derived and their behaviour with pressure and field strength analysed for cathode initiated breakdown. From this, a critical energy criterion for breakdown is obtained. Comparison is made with experimental results for water, salt solutions, and the liquid noble gases and for pulse durations in the microsecond and sub-microsecond time scales. This model serves to elucidate the dynamics of pulsed breakdown of liquids.

https://iopscience.iop.org/article/10.1088/0022-3727/28/1/025/pdf

Development of pulsed dielectric breakdown in liquids

Foreword. Preface. Acknowledgements. 1 Introduction. 1.1 Units and Definitions. 1.2 Brief History of Noble Gas Detectors. 2 Noble Fluids as Detector Media. 2.1 Physical Properties of Dense Noble Gases. 2.2 Energy Dissipation in Noble Gases. 2.3 Ionization Clusters and Principal Limitations on Position Resolution of Noble Gas Detectors. 2.4 Ionization and Recombination. 2.4.1 Jaffe Model of Recombination. 2.4.2 Onsager Model of Recombination. 2.4.3 Influence of a-Electrons. 2.5 Principal Limitations for Energy Resolution. 2.6 Detection of Nuclear Recoils. 2.7 Detection of High-Energy Particles. 3 Elementary Processes Affecting Generation of Signals. 3.1 Collection of Charge Carriers. 3.1.1 Charge Carrier Drift in Gases Under High Pressure. 3.1.1.1 Drift of Electrons in Gases. 3.1.1.2 Drift of Ions in Gases. 3.1.2 Drift of Charge Carriers in Condensed Phases. 3.1.2.1 Drift of Electrons in Condensed Phases. 3.1.2.2 Drift of Ions and Holes in Condensed Noble Gases. 3.1.3 Charge Carrier Trapping. 3.1.3.1 Electron Attachment in Liquids. 3.1.3.2 Charge Trapping in Solids. 3.2 Electron Multiplication and Electroluminescence. 3.3 Charge Carrier Transfer at Interfaces. 3.3.1 Quasifree Electron Emission. 3.3.1.1 Thermal Electron Emission. 3.3.1.2 Hot Electron Emission. 3.3.1.3 Transition of Quasifree Electrons Along Interface. 3.3.2 Electron Emission From Localized States. 3.3.3 Transitions Between DifferentMedia. 3.3.4 Ion Emission from Nonpolar Dielectrics. 3.3.5 Electron Emission into Nonpolar Dielectrics. 3.3.5.1 Electron Emission From Cathodes. 3.3.5.2 Electron Injection Through the Free Interface. 3.4 Properties of Noble Gas Scintillators. 3.4.1 Primary Processes. 3.4.2 Emission Spectra. 3.4.2.1 Emission Spectra of Gases. 3.4.2.2 Emission Spectra of Liquids and Solids. 3.4.3 Absorption and Scattering. 3.4.3.1 Self-Absorption. 3.4.3.2 Impurity Absorption. 3.4.3.3 Scattering. 3.4.4 Scintillation Light Yield. 3.4.5 Refractive Index. 3.4.6 Decay Times. 3.4.6.1 Decay Times of Gases. 3.4.6.2 Decay Times of Liquids and Solids. 4 Scintillation Detectors. 4.1 High-Pressure Noble Gas Scintillation Detectors. 4.1.1 Single-Channel Gas Scintillation Detectors. 4.1.2 Multichannel Gas Scintillation Detectors. 4.2 Condensed Noble Gas Scintillation Detectors. 4.2.1 Scintillation Detectors Using Liquid Helium and Condensed Neon. 4.2.2 Scintillation Detectors Using Liquid Argon, Krypton and Xenon. 4.2.2.1 Single-Channel Noble Liquid Scintillation Detectors. 4.2.2.2 Multichannel Noble Liquid Scintillation Detectors. 4.3 Development of Scintillation Calorimeters. 4.3.1 Granulated Scintillation Calorimeters. 4.3.1.1 UV Light-Collecting Cells. 4.3.1.2 Light-Collecting Cells withWavelength Shifter. 4.3.1.3 Scintillation Calorimeter LIDER. 4.3.2 Barrel Scintillation Calorimeters. 4.4 Time-of-Flight Scintillation Detectors. 5 Ionization Detectors. 5.1 Generation of Induction Charge. 5.2 Diode Ionization Chamber. 5.3 Triode Ionization Chamber. 5.4 Multilayer Ionization Chamber. 5.5 Ionization Chamber with Virtual Frisch Grid. 5.6 Time Projection Chamber with Scintillation Trigger. 5.7 Use of Both Ionization and Scintillation Signals. 6 Proportional Scintillation Detectors. 6.1 Gaseous EL Detectors with Parallel Plate Electrode Structure. 6.1.1 Gas Proportional Scintillation Counters. 6.1.1.1 GPSCs with PMT Readout. 6.1.1.2 GPSC with Photodiode Readout. 6.1.1.3 GPSC with Open Photocathode Readout. 6.1.2 High-Pressure Electroluminescence Detectors. 6.1.3 Imaging Electroluminescence Detectors. 6.1.3.1 Analog Imaging Electroluminescence Detectors. 6.1.3.2 Digital Imaging. 6.2 High-Pressure Xenon Electroluminescence Detectors with Nonuniform Electric Field. 6.2.1 Cylindrical Proportional Scintillation Counters and Drift Chambers. 6.2.2 Gas Scintillation Proportional Counters with Spherical Electrical Field. 6.3 Multilayer Electroluminescence Chamber. 6.4 Liquid Electroluminescence Detectors. 7 Two-Phase Electron Emission Detectors. 7.1 Emission Ionization Chambers. 7.2 Emission Proportional Chambers. 7.3 Emission Spark Chambers. 7.4 Emission Electroluminescence Detectors. 7.5 Vacuum Emission Detectors. 7.6 Further Developments of Two-Phase Detectors. 8 Technology of Noble Gas Detectors. 8.1 Selection of Materials and Mechanical Design. 8.1.1 Metals. 8.1.1.1 Construction Metals. 8.1.1.2 Sealings. 8.1.2 Insulators. 8.1.3 Feedthroughs. 8.1.3.1 Electrical Feedthroughs. 8.1.3.2 Optical Fiber Feedthroughs. 8.1.3.3 Motion Feedthroughs. 8.1.4 Electrodes. 8.1.4.1 Active Cathodes. 8.1.4.2 Grids. 8.1.4.3 Multilayer Structures. 8.1.4.4 Amplifying Electrode Structures. 8.1.5 Viewports andWindows. 8.1.5.1 Materials. 8.1.5.2 Optical Windows for High-Pressure Detectors. 8.1.5.3 Glass Machining. 8.1.6 High-Pressure Vessels. 8.1.7 Cryogenics. 8.2 Processing High Purity Noble Gases. 8.2.1 Pretreatment. 8.2.2 Pumping. 8.2.3 Baking. 8.2.4 Handling. 8.3 Purification. 8.3.1 Impurities. 8.3.2 Chemical Methods of Purification. 8.3.3 Electron Drift Purification Method. 8.3.4 Spark Purification. 8.3.5 Separation of Noble Gases. 8.3.6 Circulation. 8.4 Monitoring the Working Media. 8.4.1 Electron Lifetime. 8.4.2 Optical Transparency. 8.4.3 Mass and Position of Free Surface. 8.4.4 Temperature, Pressure, and Density. 8.5 UV Light Collection. 8.5.1 Reflectors. 8.5.2 Wavelength Shifters. 8.5.2.1 Wavelength Shifters Dissolved in Noble Gases. 8.5.2.2 Solid Wavelength Shifters. 8.6 Photosensors. 8.6.1 Photomultipliers. 8.6.1.1 Low Temperature. 8.6.1.2 PMTs for High Pressure. 8.6.2 Semiconductor Photodiodes. 8.6.3 Open Photocathodes. 9 Applications. 9.1 Astronomy. 9.1.1 Instrumentation for X-ray Astronomy. 9.1.1.1 Gas Imaging Spectrometers On-Board ASCA. 9.1.1.2 High-Pressure Gas Scintillation Proportional Counter at BeppoSAX. 9.1.1.3 High-Pressure Gas Scintillation Proportional Counter On-Board HERO. 9.1.2 Instrumentation for Gamma Ray Astronomy. 9.1.2.1 KSENIA On-Board MIR Orbital Station. 9.1.2.2 LXeGRIT Balloon-Borne Compton Telescope. 9.2 Low-Background Experiments. 9.2.1 Direct Detection of Particle Dark Matter. 9.2.2 Neutrino Detectors. 9.2.3 Double Beta and Double Positron Decay Search. 9.2.3.1 Experiments with Active Targets. 9.2.3.2 Experiment with a Passive Target. 9.2.3.3 Double Positron Decay Experiments. 9.3 High-Energy Physics: Calorimeters. 9.3.1 Ionization Calorimeters. 9.3.1.1 Liquid Argon Calorimeters. 9.3.1.2 Liquid Krypton Calorimeters. 9.3.1.3 Xenon Calorimeters. 9.3.2 Scintillation Calorimeters. 9.4 Medical Imaging. 9.4.1 X-ray Imaging. 9.4.1.1 Analog X-ray Imaging. 9.4.1.2 Digital X-ray Imaging. 9.4.2 Single-Photon Emission Computing Tomography (SPECT). 9.4.2.1 Liquid Xenon Detectors for SPECT. 9.4.2.2 High-Pressure Noble Gas Detectors for SPECT. 9.4.3 Positron Emission Tomography (PET). 9.4.3.1 Liquid Xenon TPC with a Scintillation Trigger. 9.4.3.2 Liquid Xenon Scintillation Time-of-Flight PET. References. Index.

Noble Gas Detectors

Electron recombination in liquid argon (LAr) is studied by means of charged particle tracks collected in various ICARUS liquid argon TPC prototypes. The dependence of the recombination on the particle stopping power has been fitted with a Birks functional dependence. The simulation of the process of electron recombination in Monte Carlo calculations is discussed. A quantitative comparison with previously published data is carried out.

Study of electron recombination in liquid argon with the ICARUS TPC

We have constructed and operated a 3 ton liquid argon time projection chamber as part of the R&D programme for the ICARUS project. We report on the analysis of events from cosmic rays and from radioactive sources collected from June 1991 to June 1993. We have systematically investigated the performance and the physical parameters of the detector. We present here the results obtained from the analysis of the cosmic rays data on the following items: the electron drift velocity, the electron lifetime, the free electron yield, the electron diffusion coefficient, the space resolution and the particle identification capability. The data from radioactive sources are used to study the energy resolution in the MeV range. The in depth understanding of the basic physics aspects of the liquid argon TPC allows us to conclude that such a detector can be built in large sizes and reliably operated over long periods of the time, providing a new instrument for physics experiments.

/pdf/performance-of-a-three-ton-liquid-argon-time-projection-3lwyerrscr.pdf

Performance of a three-ton liquid argon time projection chamber

A large area, gas scintillation proportional counter

A gas scintillation proportional counter has been constructed for use in detecting subkiloelectron-volt X-rays from cosmic sources. Over a sensitive area of 5 cm2, this instrument has a measured energy resolution of 85 eV (FWHM) at 149 eV. This is significantly better than similarly sized solid state detectors. Rise-time discrimination is used both to reject space background and to reduce low energy noise below 50 eV. The development of an imaging capability for this instrument is discussed.

A High Resolution Gas Scintillation Proportional Counter for Studying Low Energy Cosmic X-Ray Sources

An intrinsic energy resolution of 26+or-2 keV has been measured for the 976-keV conversion electrons of a /sup 207/Bi source in a gridded ionization chamber filled with pure liquid argon, at a drift field of 11 kV-cm/sup -1/. The measurement of the /sup 207/Bi spectrum at different electric fields was repeated several times, with very-good liquid purity and optimized chamber geometry, reproducing the results. Data were also taken with a xenon-doped liquid argon filling in an attempt to improve the resolution. Enhanced ionization was observed as expected from the presence of excitons in liquid argon, but there was no improvement in the energy resolution. It is shown that the data are consistent with the assumption that recombination straggling from low-energy delta electrons, produced abundantly along the path of the primary ionizing particle, is mostly responsible for the degraded experimental resolution. >

Delta electron production and the ultimate energy resolution of liquid argon ionization detectors

The problems of developing large-area, gas-scintillation proportional counters with high resolution are considered. It is found that simple large-area, parallel-grid proportional counters suffer from a variation in gain over the counter window. Some success has been achieved in overcoming this problem by focusing the charge cloud as it drifts into the multiplication region. Measurements are reported for various mixtures of argon and xenon as well as pure xenon.

Recent Developments in Parallel-Grid, Gas-Scintillation Proportional Counters

Multiwire proportional counters with 1 ?m polypropylene windows, of dimensions 75 mm × 75 mm and 100 mm × 100 mm, have been built to map soft cosmic X-rays. The counters are constructed with a large drift region which allows us to use the center-of-gravity technique to improve the counter's efficiency and position resolution. Using 330 Torr of propane as the gas fill and an anode plane composed of 20 ?m diameter, gold-plated tungsten wire spaced 1 mm apart, we have achieved a position resolution of better than 280 ?m (FWHM) in two orthogonal directions at an X-ray energy of 0.94 keV.

W. H.-M. Ku

Papers

A large area, gas scintillation proportional counter

A High Resolution Gas Scintillation Proportional Counter for Studying Low Energy Cosmic X-Ray Sources

Delta electron production and the ultimate energy resolution of liquid argon ionization detectors

Recent Developments in Parallel-Grid, Gas-Scintillation Proportional Counters

A Drift Multiwire Proportional Counter for Cosmic Soft X-Ray Imaging